Vacuum tube amplifier



VACUUM TUBE AMPLIFIER Filed Oct. 4, 1943 3 Sheets-Sheet 1 INVENTOR 7/1552 5. STREET Feb.3, 1948. J. c. STREET 2,435,331

VACUUM TUBE AMPLIFIER Filed 001;. 4, 1943 5 Sheets-Sheet 2 FIG. 2

IN VE N TOR JHBfZ C. ST/Eff! Feb. 3, 1948. J, STREET 2,435,331

VACUUM TUBE AMPLIFIER 3 Sheets-Sheet 3 Filed Oct. 4, 1945 IN VE N TOR Patented Feb. 3, 1948 VACUUM runs AMPLIFIER Jabez C. Street, Belmont, Mass., assignor, by mesne assignments, to the United States of America, as represented by the Secretary of the Navy Application October 4, 1943, Serial No. 504,924

6 Claims. (Cl. 250-27) This invention relates to vacuum tube amplifiers and particularly to high frequency amplifiers having a wide range.

One of the objects of the invention is to provide a wide band, high frequency amplifier with two or more stages of amplification in which all of the tubes are on at the same time and off at the same time.

Another object of the invention is to provide a high frequency, wide band amplifier of the above type in which high amplification may be obtained.

Another object of the invention is to produce amplification at high voltage and high power levels with great efficiency.

Another object of the invention is to provide a circuit for a thermionic tube in which the potential of the cathode is caused to vary with the plate-cathode current of the tube without altering the grid-cathode potential difference.

A more specific object of the invention is to provide an amplifier consisting of two or more stages in which the input of one stage is obtained from the cathode circuit of the previous stage in such a way that high amplification is realized.

Still another object of the invention is to provide a complete pulse-forming and amplifying circuit for producing discrete pulses spaced at predetermined time intervals at unusually high efficiencies.

Other objects and objects relating to the manner of arranging and connecting the various parts of the circuit will be apparent as the description of the invention proceeds.

The invention is illustrated in the accompanying drawings in which:

Fig. 1 is a circuit diagram of a transmitter and associated pulse-forming and driving circuit incorporating the invention and arranged to cause the transmitter to transmit a succession of timed discrete pulses of highfrequency oscillations;

Fig. 2 is a circuit diagram of a modified form of the circuit of Fig. 1; and

Fig. 3 is a circuit diagram of another modification of the invention in which a plurality of stages are used for greater power output.

In conventional forms of resistance-capacity coupled amplifiers each stage reverses the polarity of the signal from the stage before it. Where it is desired to amplify a single pulse, if the first tube of such an amplifier were arranged'to conduct when the pulse was transmitted, then the second tube would be shut off during that period, the third tube would conduct, the fourth tube would be shut off, and so on. At the end of the pulse the first tube would shut off, the second tube would then conduct, the third tube would shut ofi, the fourth tube would conduct, and so on. This means that when no pulse is being transmitted, alternate tubes are conducting and consuming plate circuit power. Where discrete pulses are being transmitted which are separated from each other a greater time duration than the duration of one pulse, half of the tubes are on during the period when no pulse is transmitted, and since this time is greater than the period of the pulse, a great deal of energy may be consumed without producing a beneficial result. The amplifier of the present invention provides that all of the tubes are shut ofi when no pulse is being transmitted and all are on when a pulse is being transmitted, and this is done without loss of amplification.

In general, the invention comprises, as a principal feature, an amplifier in which a tube is provided with a resistance in its cathode circuit and the output of the tube is taken from across this resistance, as it is in a cathode follower circuit, but, unlike the cathode follower circuit, the grid of the tube is caused to rise and fall as the potential across the resistance rises and falls without affecting the potential difierence between the grid and cathode of the tube caused by a signal applied to the grid.

' In the circuit shown in Fig. 1, a gas tube I0 andassociated circuit delivers a positive square pulse of a predetermined time duration to the grid circuits of three tubes ll, l2, and [3 which are connected in parallel. This pulse is amplified in the tubes H, I2, and I3 and delivered, still as a positive pulse, to the grids. of two amplifier tubes l4 and [5, arranged in parallel. These tubes reverse the polarity of the pulse and drive a transmitting oscillator tube l 6 which is so arranged and connected in the circuit that it will transmit only during the period of the negative pulse. Tubes ill to I6 inclusive are either all on or all ofi at a given time.

The tube l0 may-be of the type in which the grid has control of the tube only when the tube is not conducting. As shown, this tube has a plate I9, a control grid 26, and a cathode 2| which is heated by a, heater 22, the latter being energized by a source of alternating current from the secondary of the transformer 23 which is shown under the tube 13. The letters X-X indicate the heater connection the circuit of which has been omitted ,to'avoid confusion.

A positive trigger pulse, indicated at 25, from some suitable pulse-forming circuit (not shown), is fed to the grid 20 through a condenser 26 and a relatively high resistance 21 which is provided for a purpose to be hereinafter explained. The plate I9 has connected to it a,,network, 28 which I may comprise :a'plurality of r sections" oi sinj ductances "29 and condensers '30. The "inductances 29 may be equal in value. The condensers 30 also may be equal in value with the excep tion of the end condensers which may have :a p

Value of one half the capacity otthe others. One end of the series inductahc I w 28 is connected to the plate liieg the tubeflli and this same end, or any point along the series inductances, is connected through a relativelyhigh resistance 3| to a positive "source -of-potenti-alwhich will be described later. The commongjunc i ture of the condensers in the network 28 is connected through a cathode resistance 32 to the cathode 2| of the tube to; Thegvaiceiorthe resistance 3| shoul'dbe such that, taken in connection with the conductances of element circuit of the tubes ii, l2, and 13, the iimpeeanee'or the circuit across the network 28 will "be substan the tube It, the tube becomes conductive and the condensers 30 start to discharge through it and through the resistance 32. The effect of the inductances 29 and condensers 30 ,:in the-network 28, is to cause a potential toyappear across the resistance 32 which "is equal :to'JJone half of the voltage to which the condensers 30 were charged. A. voltage wave-'frontnthen:travels towards the right to the open end ..of :the network and is 1 8-1 fiected back toward -.the plate 19 and resistance 32. During the time this wave is traveling, the

voltage across the resistance 32rmains at the same value, but when the wave reaches the "plate l9 and resistance 32 again, the voltage ac'ross'the resistance 32 is reduced tozero, which causes the tube It to shut 161T and beplacedunder cong f trol of its grid 20 again. Thus,"a, positive-square pulse of a time duration determined by the component parts of the network '28 is produced across the resistance 32. Such a pulse-forming network is shown and described in the'applic'a ti'on of J. C.'Street, Serial No. 479,660, filed March 18, 1943. Other pulse-forming networks "which may be usedvare shownand described in the application of Ernst A. Guillemin, Serial No 492,160, filed July '6, 1943. The pulse'forming circuits disclosed in the latter'reference are also of the lumped constant type, the elements being so arranged such that a uniform transmission line is simulated. A source t: charging voltage is connected to the artificial line, and a switch tube is provided to initiate the 'charging and discharge of the line.

The cathode 2| of the tube I is connected through a large coupling condenser-33 and a re-' sistance 34 to a common conductor 35 forthe grid circuits of the tubes ll, |2, and l3. These tubes, in the particular arrangement shown, are beam power amplifier tubes=andthe grids 33,31; andi38 of the tubes l l, l2,'a'n'd l3; respectively, are connected respectively through small gi'id ''resistances 39, 40, and 4|, for suppressing parasitic oscillations to the common grid connection 35. The cathodes 42, 43, and 44 of the tubes H, l2, and I3 are connected together and to the end of the cathode resistance 32 which is not connected to the cathode 21 of the t be Hi; It Will thus be seen that the cathode resistance 3i 2;;is connected betweenthegrids of the tubes l1, l2, and I3 and the cathodes of those tubes, and hence the posi- "tive pulse which appears as an increase in the "ii'ipfiitential'Zdifference across this resistance 32 will it I an a u fie catiicue resistaricewa to a constant potential point d i on the power supply which will be de' increase in the potential difgrids and cathodes of the :43, and 44 of the tubes ll, l2, connected through a common sfibdlalter, and through aresistance 49, which s a a t of haizo e u l r o ground, asjin'dicatedi at50 f These'rcathodes are 'hea'tedby heaters 5'2,53,' an'dtiwhichjareelectrically con; nected to .the cathodes d'jwhichderive energy frorn'the 'se'con' ar y oi theftransfor'mer 23;.as indicated bytheittemfX-XQ the wiring for the heatersoi 't'heft'ubes .1 and 'l'2' havi ng been omitted toavoidconrusion.

Th cathodes of the tubesfl'l ,fl2, and 13 are also connected'thiiou'gh glfidresistances '56fand 51:"to theiigrids 58" and ts 'ofithe tubes 14 and 15, respectively; These amplifier tubes Imay be of the type having filamentary cathodes till and 6"l, ,respective1"", whichi'are, energized from .the

- secondary of a Ttr'an'sformer 32,. the connections being indicatedby the lettersY-Y. The midpoint f 013' each ,Tof. ithese filaments is connected throughfa comrnonlresistance 53'to ground, as shown It'uiillbeseenthat the grid circuits of the tubes l4 andlfi.are connected across the cathode resistance' 48 which appears in the circuit, which is common toithelcathodes .of the tubes ll, I2, and I3, and hence any difference in potential whichis produceq across this resistance willalso appear between the cathode and grid ofeachpf the tubes l4 and l5, 7 I .7 The-positive pulse appearing on the grids of-the tubes] l, l2,,a nd;l3 willcause these tubes to conduct duringthe pulse which will produce a cer-; tain' potential difference for the periodof'tl'ie pulse across theresistance '48, and thus produce a'pos'itivepulseupon the gridsof the tubeszM and i5; causing these tubes also to conduct during the time of thepulse. Theplates 6B. and B1 of the tubes hi and; l5 are suppliedwitha positive potential through low resistances 163 and 69, respectively, which zare used tosuppress parasitic oscill ations, since thetubes are in pa'ralleLand through the common load resistance "l0- -froma source of potential to be described later.

. The tube l6 maybe ahigh-frequency oscillator, as, for instance, a magnetron an'dthe plates of the tubes I4 and i5 maybe connected respectively through the resistances-68 and 69 and a condenser 13 .t0the cathode 12 of the'tubelli. The tube' lfi has one side of its heater 14 connected' 'to'the cathode I2, and the heater is energized from the secondary of a suitable transformer 15, the primary of which is well insulated from the sec? ondary andiis connected to a source of a-lternat ing current. The plate 18 of the tube 16 is connectedto'ground, as :shown, .and-ia bleeder resis'-' tance 19, in "parallel wi-th.. an inductance 80,-' is connected betwcen the cathode 12' -aEnd 'theplate '18; The high-frequency energy is led off by means of the pick-up loop 8| and coaxial line 82. The tube I6 is operated preferably with its anode connected to ground, as shown, because this type of tube is usually made with the anode forming part of the metallic shell of the tube. Hence it would be diflicult to insulate the anode from ground and to eliminate the effect of the large capacity between the shell of the tube and ground.

The condenser 13 is normally charged, and when the tubes I4 and I5 become conductive during the period of the pulse, the condenser 13 discharges through the tubes I4 and I5 and through the tube I6, thus causing the tube I6 to oscillate. The potential across the condenser 13 when charged may be in the order-of ten.thousand volts or more. v

There is some distributed'capacity to ground in the cathode of the magnetron tube I8 and in the wiring connected to the cathode. This capacity tends to charge during the pulse and to discharge across the magnetron tube at the end of the pulse, with the result that insteadof a sharpcut-off of the pulse, the end of the pulse is caused to trail ofi as the capacity discharges. This capacity has been illustrated by the condenser 83, shown in dotted lines from the cathode to the plate of the magnetron tube. The inductance, 88 is provided to help discharge this capacity at the end of the pulse. When the value of the inductance 88 is properly chosen, the end of the pulse will produce a voltage surge which will be applied across the capacitance 83 in the opposite sense to the charge thereon, causing the capacitance to discharge quickly. In order to prevent an oscillation being set up in the circuit of the inductance 88 and stray capacitance 83, the resistance 19 is provided to damp out this circuit. In place of the resistance 19 a diode thermionic tube may be used with the plate connected tothe cathode of the magnetron and the cathode of the diode tube connected to the plate .of the magnetron. I

In order to produce the plate voltages for the tubes I8 to I3 inclusive and the grid biases for these tubes I utilize two half-wave rectifier tubes '85 and 86. These tubes are arranged so that the tube 86 will produce several hundred volts above ground for the plates of the tubes II, I2, and I3, while the tube 85 will produce over a thousand volts below ground for the cathode voltages of the "tubes I8, II, I2, and I3, and the grid bias voltages of these tubes and the tubes I4 and I5. To this end the filaments 81 and 88 of the rectifier tubes 85 and 86. are connected to separate filament windings 89 and 98, respectively, on a transformer 9|, the primary 92 of which is energized from a suitable source of alternating current. A high voltage winding 93 has one end connected to the filament winding 89 and the other end connected to a terminal 94 which forms one end of a parallel voltage divider circuit, one branch of which includes a resistance 95, the resistance 49, already mentioned, and a resistance 98, con- H nected in series in the order named to a terminal 91 connected to the plate 98 of the rectifier tube 85. The other branch of the voltage divider circuit comprises resistances 99 and I88, connected in series between the terminals 94 and 91 in the order named. A filter condenser I III is connected between the terminals 94 and 91, a filter condenser I82 is connected across the resistance 96, and a filter condenser I83 is connected across the resistance I88. The potential appearing between 6 the terminals 94 and 91 may be in the order oi 1200 volts with the terminal 91 negative and the terminal 94 positive. f v

The rectifier tube 88 is connected in series with a portion of the secondary winding 93 of the transformer 9|, the plate of thetube being con-,- nectedto an intermediate point I84 on the sec ondary winding. A condenser I isconnected between the terminal 94 and a terminal I88 which is connected to the filament of the rectifier tube 86. I The voltage developed between the terminals 94 and I85 may be in the order of 508 volts with the terminal I85 being positive.

The grid 28 of the gas tube I8 is biased by connecting it through a grid resistance II1 to the negative terminal 91 on the power supply, and the common grid connector 35 for the tubes II, I2, and I3. is also connected to this terminal through a grid resistance I I8. The screen grids I23, I24, and I25 of the tubes II, I2, and I3, respectively, are connected to a terminal I81 on the power supply, which is at the juncture of the resistances 99 and I88, through a screengrid resistance I28, a by-pass condenser I 21 being cons nected between the screen grids and the cathodes. The plates I38, I3I, and I32 of the tubes II, I2, and I3 are connected respectively through parasiti oscillation suppressor resistances I33, I34, and I35 to a common plate connection I36 which is connected directly to the positive potential terminal I85. v 4

The network 28 in the plate circuit of the tube I8 receives its positive potential through the resistor 3I, which is connected between the net work and the terminal I81 which point maybe several hundred volts more positive than the terminal 41. The resistance 3| is made suificiently large so that there will not be enough voltage difference between the plate and cathode of the tube I8 to keep the tube conducting after the pulse has been formed, but this resistance is not so large as to prevent the condensers 38 in the network 28 from charging sufiiciently during the time between pulses. 1

Theplate supply for the two tubes I4 and I5 is furnished by four half-wave rectifier tubes I38, I39, I48, and MI, arranged in a bridge circuit.

The filaments of these tubes and the high voltage is supplied from two separate transformers I42 and I43, -respectively,so as to be able to control the high voltage independently of the filaments, and the output of this power system is connected across a bleeder resistance I44. The negative end of this resistance I44 is grounded, as at I45, and the load resistor 18 is connected between the positive end I46 and the juncture of the resist.- ances 68 and;69 in the plate circuits of the tubes and I5. i The stray capacities to ground of the input circuit of the tubes I4 and I5 and the grid-cathode capacitances of these tubes may tend to prevent the rapid drop of the potential of the grids of these tubes at the ends of the pulses. In order to discharge these stray capacitiesat the end of each pulse to give a short cut-off, a gas tube I58 may be provided with its plate I5I connected to the grid circuit of the tubes I4 and I5 through a resistance I52, and the filamentary cathode I53 connected to the terminal 41 on the power supply through a cathode resistance I54. A condenser I55 is connected across the resistance I54 and a I hence the drop in potential across the resistances 32 and 48 appears between the grid 20 and cathode 2I of the tube I during the pulse. Since the tube III is conductive during the pulse, the resistances 21 and II 1 also perform the important function of preventing the shorting of the pulse between the grid and cathode of the tube III.

It will be seen that all of tubes III to I6 inclusivein the pulse-forming and amplifying circuit oi Fig. 1 are on during the period of the pulse and are ofi between pulses.- It will also be seen that. since the potential of the grids of the tubes II, I2, and I3 rises with the cathodes of those tubes, the signal causes no decrease of the potential of the grids with respect to the cathodes. Thus, in addition to the tubes all being on during the pulse, the circuit still amplifies and a high gain may be obtained from it. The amplifier of the invention therefore, becomes especially useful where discrete pulses, spaced at predetermined time intervals, are produced, and economy of operation can be obtained with great amplification.

Where the circuit of the invention is used, as

I is shown in Fig. 1, to operate a high-power output device, such as the magnetron I6, the parallel tubes II, I2, and I3 must normally have a large negative potential on their grids and these grids must quickly rise in potential during the pulse to a large positive potential. A conventional amplifier would not fulfill this requirement unless an extremely high amplitude square driving pulse were available to apply to the grid of the amplifier. This pulse might be in the order of 12O0 volts positive. In the circuit of the invention both the cathodes and grids of the tubes II, I2, and I3 are negative by a large amount, there being just enough difference in potential between the cathodesa'nd grids to keep the tubes normally cut oil. A positive pulse in the order or about 250 volts applied to the grids of these tubes will raise their potential far enough above the potential of the cathodes to cause the tubes to conduct, thus raising the potential 01 the cathodes towards the potential of the plates. By back-coupling from the cathodes to the grids of the tubes through the large coupling condenser 33, which presents negligible reactance to all frequency components in the repeating pulse spectrum, the grids rise in potential with the cathodes but maintain the potential separation between them and the cathodes during the pulse by the magnitude of the original pulse applied therebetween. All of this is done with great eiliciency.

The gas tube acts, in the illustration shown, as a switch which is capable of being operated by a trigger voltage pulse and which is used in the circuit because of its functional part in the pulse-forming operation.

It may be seen that the change in potential at the cathodes of tubes H, I2, and I3 with the pulse is equal to the arithmetical sum of the potentials of points 41 and I06 less the voltage drop in one of the tubes II I 2, or I3 and in its corresponding plate resistor I33, I34, or I35.

It may be further noted that the resistor 48 isolates a preceding portion of the circuit consisting principally of tubes III, II, I2, and I3 and their associated circuit components, from the potential of point 41 as a result of the voltage drop in the resistor 48 during the pulse. This portion of the circuit is therefore raised in potential during the pulse. In Fig. 2 I have shown a modified form of the invention, although operating on the same gen-. eral principles. which may be similar to the gas tube III of Fig. 1, has its grid I63 connected through a resistance I64 to the cathode I65 of a diode tube I66. The trigger pulse is delivered to the plate I61 of this diode tube. The cathode I65 of this tube is connected through resistances I66 and I69 to a. source of negative bias potential, indicated at I10. This provides the bias for the grid I63.of the tube I62. The plate I'61 of the diode tube IS S-is also connected through a resistance "I. to the source of negative potential I10. Thus connected, a positive pulse received on the plate I61 of the diode tube I66 may pass through the tube because of the rectifying action thereof and will appear directly on the grid I63. However, a positive pulse produced on the grid I63 by the action of the circuit following the tube I 62 can not pass through the tube I66 to affect the trigger-pulse-producing circuit. The diode I66, therefore, performs the function of a buffer circuit. Grid current in tube I62 i limited to allowable values by the resistances I64, I68, and I69.

The gas tube I62 has a cathode I12 which is. connected directly to the grid I13 of a driver tube I14. The heater I15 for the cathode I12, which is shown connected to the cathode, may be energized from thesecondary of a suitable transformer I16, the primary of which is con-Q nected to a source of alternating current. The cathode I12 is also connected through a cone, denser I11 to the juncture of resistances I68. and I69 in the grid circuit of the tube I62.

In order to bias the grid I13 of the tubev I14, this grid is connected to a source of negative bias potential, indicated at I18, through an m5 ductanoe I19, a resistance I80, and another re sistance I8I,- arranged in series in the order named.

The plate I82 of the tube I62 is given a pos itive potential through a resistance I83 fromja source of potential indicated at I84. A con-. denser I85 is connected between the plate I821 of-the tube I62 and the juncture of. resistances I80 and I8I.

The tube I14 is shown as a screen grid tube having a filamentary cathode I86 which is on ergized from the secondary of a transformer I81 whose primary is energized from a suitable, source of alternating current. The cathode I86 isoonnected by means of a condenser I88 to the, juncture of the resistances I80 and I8I, and the] cathode is also connected through an inductance I89 to ground.

The plate I90 of the tube- I14 is connected through a plate resistance I9I to a source of positive potential, indicated at I92, the plate being also connected through a bY-Dass con- .denser I93 to ground. The screen grid I94 of -this tube is connected through a screen resist I ance I95 to a source 01' positive potential, .-dicated at I98, the screen grid being alsoconnected to the cathode through a by-pass cone denser I91. The output of this circuit is through a condenser I98 which is connected to the cath-' ode I66 of the tube I14.

In the operation of this circuit the tube.

connected in series with the resistance I83 and the resistance I8I across the positive and ne In this circuit a gas tube I62,

I62 .is normally non-conducting. Under such a con- 'dition the condenser I85 is charged since it is' zi feees'sr diode tube I 60 from a suitable circuit which pro This positive pulseducesu the. trigger" pulse;- passesthrough theplate-cathode circuit of-the diode tube I60 and isimpressed' upon thegrid" l6 3 of the gas tube I622 This grid'is' thus swung ir'i'the positiveidirection' withresp'ectto the cath ode H2 above the critical potential and the tube becomes conductive'ythus' taking 'the control awayirom'thegridz A's scone-as the'tube? 102"starts to conduct, the condenser: i851discharges'through the-tube and; through the inductance I 19* and resistance l 80; The grid I13ofthe'tubeilT4 was--at the potential oflthe negative source I18; butimmediatelyswings" in the positive direction because'oi' the" voltage now" applied across" the inductance I and'therresis'tance" I805 The*values of the inductance l 19' and resistance l 80"are chosen so that. the action of thecondenser I85 in dis-- charging through this circuit will produce in effect a positive pulse with-steep leading and trailing, edgesfon' the grid I13 of the tube 1T4; causingx it' to draw grid" current.

The positiyepulse on th grid of the'tube'il 14 causes this tube to. conductand the plate=cathdenser 20'5 -to the gridsof the tube '204through action, in the plate-cathode'circuit-V of the tube I62. 7 n j v 1 Y Theca'thode I12 of ithetube [62 aisorises with the grid 1 T3 and produces airise inipotenti'al of the grid" l63'by"virtueof the" coupling through V the condenser III. This prevents thegridfllii ofith-ei ga' ltube trom'becoming so negative with respect to the cathode as tojaffct the conductft'ity of the tube b'eforeithe pulsehas been compieted"; t t or The inductance I8'9"may'beusedin the'cathcde circuit of the driver tube only when it; presents-a high reactance to" the frequency'components oi the signalsiused to operate the: circuit: When thi'sf condition is satisfied; the inductance will push the cathode up in 'potential with the signal Variations. g V n n v I In; the circuit of Fig. 2" it will-be-seenthat the tubes I62 and lld'are'bothflonduring thepulse andofi between pulses, and" it will be seenaiso that the output may be taken from the'cathode er't ietube 114* with tic-sacrifice of" gain. 1 t or some instances where greater power is desired additional stages ofithecircuit of the inven tion' maybe used: Inysuch a caseallf'stages-exce t the last fare" caused, to; rise and fall 'in potential with the potentialf of'thef cathodeof the amplifier tube "in the last stage; The circuit of 3 illustrates such arr'eirrange'ment; Inthis circuit the trigger pulse passes through? a diode 200" and is applied t'o the grid of a gas tube 20? The plate circuit of theftube 2 111 is provided with a network 202 similar to that: shown ii'rFig: 1, for producing a square pulse wheni the tube 2 0! is ma'd'e conducting-"which pulse" may be 351:1'ustieii"in time"duration Icy switching in orout sections 'ofth'e net-work; This-network. is CORE rie'ct the tube EM -and a resistanc'e 203 1 1%? in? the cathode: 'ciiicuiti thereof; The resistan as 203 also connected ib th'einput cm cuit' of a screen grid tubel 04,the cathodeoiithef tube20 i being connected -through a coupling conparallel resistances 206 and 201, while the other:

- endof'the resistance-2031s connected directly: tothecathode ofthe tube 20 i; A resistance 208? isprovided' in the cathode circuit of the tube 204; across-which resistance the output of the-r first stage-is taken.

The" gas tube 20l' andfthe- .tube 204 are connected imilarlyto the circuit of -Eig; 1, the potens tial of'the gas tube 20l-being'free to rise andsfali as the potential (inference-across the resistance I have found it desirableto enclose:

208 varies I V the tubes 200, 20'l,and' 204 and alsovthe network 202 iand associatedcircuits within 'a-metal 'contamer-210i which forms an" electrostatic shield for these components and a convenient auxiliary ground which is isolated from the imain ground connection; Thevarious leads for supplying potentials tothe circuit arefiltered: with resist ances an'd" condenserszas :thev pass :throughiopena tube 204 i'siconnected through thesresis'tance' 208' to th'econtainer;asshown at z'l'lz' a the arrangement shown the containerr 2:10

is now* arranged'fto follow the? potential; offthe cathodes ofj'anot herstage -of alm'plificatio'n2; This 7 other stage'may comprise two twinamplifientubes 2| 2 "an'd"2 |3 connected imparalleLwith th'eicathe odes thereof connected: tog'etiieri and; to ground through" a resistance 2 t4 shunt'diby a choke 21 5';

The container" 2 10 1s connected'i by: 'nieansof thewire 2 16 tothe'fcathode's of th'tub'es- 212 and 213, while the cathode; ofthe tubet 2041 isafc'orinected through. a coupling condenser-2 2| 1f 't'0' the grids: of the tubes: 212' and 213- through':. parablei: resistors 218- and' 218'; for the tube: 212;. and 220'and' 2 2l; for the tube 2 l3i I The separate: circuit" asSO'ciatd with? the 1 tubes 212" andi'2il3; together witlifthc container 210;

is then:- enclosed in" as: container 224 the con tainer' 224' being connected: to: ground and all of the leadsfor both circuits bei'n'g filtered with resistances and condensers as thy 'pa'ss through openings iir-thecontainer-124": The output or the? circuit is obtained" from the cathods or: the tubes2ii 2 andi'2-l3 through a condenser 2251' the outputbeing indicated at 2'26i The-purpose of 'thedouble shielding arrtingev ment of Fi'g 3- i's:to: prevent any tendency toos'cil late which may: be" caused by "the screen grids of the tube 204 being: connected together within butzhighiimpedanceto the higher" frequency c'dmpcnents ofthe'squarepulse produced by the' tiibe 20-1: and associated circuit, thus" adding to the effect of the diode tube 200: to isolate'the'tube 2.0.1 from the pulse-producing ici'rcuit';

In the operation of this circuit a positive trigger .p'ulse delivered to thediode tube; 200; will swing the potential of thezgridvofi thetube 20lv in the positive direction; so as: to start: this tube metal conducting with negligible voltage drop. This will connect the network 202 across the resistance 203 which will cause a potential drop to appear across this resistance for a period of time determined by the network 202. The potential across the resistance 203 is applied between the grids and the cathodes of the tube 204 so as to cause this twin tube to conduct during the period of the pulse. The flow of current through the tube 204 produces a potential drop across the resistance 208 in the cathode circuit thereof, and this potential difference is applied between the cathodes and grids of the tubes H2 and M3 which are thus caused to conduct during the period of the pulse. Current flowing in the tubes M2 and 2| 3 causes a potential drop across the resistance-choke combination 2 and 2| 5, between the cathodes of the tubes H2 and 2I3 and ground. Since the resistance M4 and choke 2l5 are in the cathode circuit of the tubes H2 and 2| 3, the cathodes of these tubes will rise in potential with respect to ground in proportion to the current flowing in these tubes. But the container H is connected to the cathodes of the tubes H2 and H3 and therefore also rises in potential during the period of the pulse. The resistance 208 connected in the cathode circuit of the tube 204 is also connected between the oathodes and grids of the tubes H2 and 2| 3 and therefore these grids will rise in potential with the cathodes of the tubes 2|2 and H3. But current flowing through the tube 204 flows through the resistance 208 and produces a potential drop which causes the cathode of the tube 204 and the associated circuit including the gas tube and the grids of the tube 204 to rise in potential in proportion to the current flowing in the tube 204 and in proportion to the current flowing in the tubes H2 and 2| 3. It will thus be seen that the potential of each stage in the circuit rises and falls with the cathode of the succeeding stage. and this operates to produce amplification of the pulse formed by the network and at the same time causes the tubes to go on and 01! together. The choke 2l5 shunted across the resistance 214 acts similarly to the inductance 80 of Fig. 1 to discharge distributed capacities in the input of the load circuit and thus shorten the trailing edge of the pulse.

It will be seen from the description of Figs. 1, 2, and 3 that I have provided an eflicient wide band amplifier which has particular value for use where high power amplification is desired, especially for the amplification of discrete pulses.

Many modifications of the invention may be made without departing from the spirit thereof, and I do not, therefore, desire to limit myself to what has been shown and described except as such limitations accur in the appended claims.

What I desire to claim and secure by Letters Patent is:

1. An amplifier comprising a plurality of thermionic tubes connected together in cascade, each of said tubes having an input circuit and a cathode circuit including a resistor, the resistor in the cathode circuit of each tube being connected in the input circuit of the succeeding tube, and the cathode circuits of all tubes except the last tube being so connected to the cathode of the last tube that the potentials of these circuits can rise and fall with the potential of said last cathode.

2. An amplifier comprising a plurality of thermionic tubes connected in cascade, each of said tubes having at least a plate, a grid, and a I4 cathode, a separate cathode circuit including a resistor for each of said tubes, said resistors being in series, arranged in the order of the associated tubes, each of said resistorsbeing connected b'etween the grid and cathode of the nextsucceeding tube, a sourceof potentials, means to apply positive potentials from said source to the plates of said tubes, and means to apply a negative potential from said source to the cathode of-th'e last of said thermionic tubes through the resistor in the cathode circuit thereof. h

3. An amplifier comprising a thermionic tube having at least a plate, a grid,'and a cathode, a cathode circuit for said tube, means associated with said cathode to raise the potential of said cathode with-respect to a predetermined reference potential in proportion to the amount of current flowing through said cathode circuit, a condenser associated with the grid of said tube, means to charge said condenser, means to initiate the discharge of said condenser, means to cause the discharge of said condenser to apply a positive voltage pulse between said grid and cathode, means to control the discharge of said condenser so as to shape the voltage pulse thus applied to said grid in a predetermined manner, means to cause the potentials of said condenser, said discharging means, and said controlling means to follow the potential changes of said cathode, and an output circuit connected to said cathode to obtain voltage variations therefrom.

4. An amplifier comprising a thermionic tube having at least a plate, a grid, and a cathode, a cathode circuit for said tube, means connected to said cathode to raise the potential of said cathode with respect to a predetermined reference potential in proportion to the current flowing through said cathode circuit, a network including a condenser connected to said grid, means to charge said condenser to a predetermined potential, a gas tube connected across said network, means to cause said gas tube to become conductive so as to permit said condenser to discharge, whereby a positive potential with respect to said cathode will be applied to said grid, means to cause the potential of said gas tube, said network and said grid to follow the potential of said cathode, but to retain said positive potential of said grid with respect to said cathode, and an output circuit connected to said cathode to obtain voltage variations therefrom.

5. An amplifier comprising a thermionic tube having at least a plate, a grid, and a cathode, a cathode circuit for said tube, means associated with said cathode to raise the potential of said cathode with respect to a predetermined reference potential in proportion to the amount of current flowing through said cathode circuit, pulse forming means associated with said thermionic tube and including a pulse forming network, a gas tube, and a resistor connected to the cathode of said gas tube, said resistor being connected between the grid and cathode of said thermionic tube, means to charge said pulse forming network to a predetermined potential, means to cause said gas tube to become conductive so as to permit said pulse forming network to discharge whereby a positive pulse is applied between the grid and cathode of said thermionic tube, means to cause the potential of said gas tube, said pulse forming network and said grid to follow the potential of the cathode of said thermionic tube, but to retain said positive potential of said grid with respect to said cathode of said thermionic tube, and an output circuit nnscteqit y h ycamo onden s r ssoc a a x h lm- 8? l Nu b r means 0 charge aid g xdensfir mean; f-f 2,120,823 ah thfifl sqharge o a, aislwndwsan w r y a 2,127,334,. ms v aq u e a l ed betweenwidi rld 78,0 2: 

